This invention is in the fields of biochemistry, pharmacology, and anti-viral agents.
The background information and teachings contained in above-cited application Ser. No. 737,169 (now U.S. Pat. No. 5,208,031) is incorporated herein by reference. That application describes topical lubricants which are spread on the surfaces of the genitals before and during sexual intercourse, which contain a water-soluble zinc salt as an anti-viral agent. The lubricant must be non-irritating, physiologically acceptable, and free of adverse long-term effects when used in this manner.
The zinc salt must release zinc ions at an effective concentration that reduces the risk of sexual transmission of herpes simplex virus from an infected person to an uninfected person (as indicated by its ability, at similar concentrations, to inhibit the infectivity or replication of herpes viruses in in vitro cell culture tests or in in vivo animal tests). Preferred organic salts include zinc acetate and zinc propionate, which are highly soluble in water, and which have low pK values (which indicates high levels of ionic dissociation to release the ion, Zn.sup.++). Other organic salts that are less preferred but which can be used if desired include zinc butyrate, formate, gluconate, glycerate, glycolate, and lactate. Another salt that may be suitable for use by some people comprises zinc sulfate; however, it causes irritation in some people, and is not preferred.
Prior to this invention, numerous researchers reported that zinc could inhibit herpes viruses in cell culture tests (e.g., Gordon et al 1975, Shlomai et al 1975, Gupta and Rapp 1976, Fridlender et al 1978, and U.S. Pat. No. 4,407,818 (Lionelle et al)) or in previously-infected people or animals (e.g., DeRoeth et al 1963, Jones 1979, Tennican et al 1979 and 1980, Fahim et al 1980a and 1980b, Wahba et al 1980, Brody et al 1981, Eby and Halcomb 1985, and U.S. Pat. Nos. 4,465,666 and 4,762,715 (Lukas et al)).
Most of that work was done before the advent of nucleoside analogs such as acyclovir and gancyclovir; interest in zinc as a topical anti-herpetic treatment dropped off sharply after nucleoside analogs offered a more effective oral treatment. Most of the above-cited reports involve zinc sulfate, which causes genital irritation in most users, and none of them disclose or suggest the use of zinc as a preventive agent for use in genital lubricants during intercourse, to reduce the risk of transmission to someone not previously infected. That type of preventive use was the subject of co-pending application Ser. No. 737,169, which is not prior art against this application.
The molecular mechanism by which zinc inactivates herpes viruses (and, apparently, the human immunodeficiency virus, abbreviated as HIV, the causative agent of AIDS) is believed to involve the formation of crosslinking bonds. Zinc, a positively charged ion, binds to unshared electron pairs on the residues of certain types of amino acids (including cysteine, histidine, glutamine, and asparagine) in proteins. This crosslinking reaction cause viruses to agglomerate, precipitate, and bind to each other and to various types of cells that cannot be infected. This reduces the ability of the crosslinked viruses to infect susceptible cells.
The foregoing is discussed in more detail in application Ser. No. 737,169 (now U.S. Pat. No. 5,208,031).
Addendum to U.S. Pat. No. 5,208,031: Physiology and Toxicology
The following paragraphs summarize (1) a major review article on zinc physiology and toxicology, which was published in early 1993, and (2) items of prior art that came to the Applicant's attention after application Ser. No. 737,169 was filed. The prior art was cited in application Ser. No. 737,169; since prior art statements are not published as part of a patent, they are summarized below, since they shed more light on the invention.
An extensive review article which discusses the molecular activities and biochemical effects of zinc was published in January 1993 (Vallee and Falchuk 1993). Among other things, this report concluded that zinc is "virtually nontoxic" inside the body. Toxicity problems can arise in unusual situations, such as inhalation of zinc fumes by metalworkers, genetic defects that render certain people unable to metabolize zinc properly, and problems related to zinc deficiency, but such problems are rare, and in healthy people, toxicity caused by excessive zinc is virtually nonexistent. Since zinc is an essential cofactor in hundreds of mammalian proteins, it is carefully regulated by the body; this is in contrast to other transition metals, such as copper and iron, which cause substantial toxicity if their concentrations exceed certain limits. If zinc in the blood exceeds preferred levels, at least two major factors reduce it to preferred levels: (1) zinc secretion in the urine and feces rises, and (2) it stimulates the expression of chelating proteins such as metallothionein, which efficiently sequester the zinc in inactive form. Zinc can also bind reversibly to numerous other proteins as well, which further helps maintain homeostatic equilibrium. These factors provide efficient mechanisms for controlling or eliminating excess zinc. As stated in another review article, "Toxicity of zinc is low . . . zinc is not mutagenic and has little, if any clastogenic properties . . . zinc is not teratogenic; it can, in fact, avert teratogenicity of other agents. Conversely, zinc deficiency may be harmful" (Leonard et al 1986). Other toxicological and physiological analyses include Vallee 1988, Mills 1989, and Bach 1981.
The great majority of zinc in the body is in cohesive tissue, primarily skeletal muscle and bone. Zinc in the blood constitutes less than 0.5% of total body zinc. About 80 to 90% of blood zinc is either inside cells or bound to cell surfaces. In the plasma, which contains about 1 ug/gram of zinc, the great majority of soluble zinc is bound to proteins such as albumin, alpha macroglobulin, and transferrin.
A few reports refer to zinc as a "heavy metal." This apparently is based on an arbitrary classification in which any metal with a molecular weight higher than iron (MW 56) is called a heavy metal. However, "heavy metal" is misleading, since it implies "toxic and dangerous" to many readers. The archetype heavy metals are mercury, cadmium, lead, uranium, and plutonium; clearly, zinc does not belong in the same category with those. Accordingly, zinc should be called a transition metal, or an essential mineral.
In addition to the Vallee and Falchuk review, which focuses mainly on zinc in blood and internal tissues, numerous reports state that zinc can help stabilize and protect cell membranes. The molecular mechanisms apparently include protecting sulfhydryl groups against oxidation, inhibiting the production of oxidative free radicals, and inhibiting the leakage of metabolites out of pores or other lesions created by certain bacteria and viruses (Chvapil 1973 and 1976; Mahadevan et al 1990; Bray and Bettger 1990; Pasternak et al 1992; Kaszuba and Hunt 1990). Zinc also increases the integrity of multicellular membranes in the body, such as blood vessel walls (Hennig et al 1992). Zinc also promotes the activity of numerous enzymes that help cells withstand stress, such as glucose transporters (Pasternak 1990), ectonucleotidases (Meftah et al 1991), and protein kinases (Zalewski 1991). An extensive review of the beneficial effects of zinc in promoting the growth of epidermal cells and the healing of skin deficits (such as cuts and wounds, decubitis ulcers (such as bedsores), rashes, and other lesions is provided in Agren 1990.
Zinc is widely used as a soothing/healing/protective agent in topical formulations that are applied to the skin, such as ointments, lotions, creams, and powders. For example, zinc is the active ingredient in calamine lotion, sunblocking creams, various anti-fungicidal or anti-bacterial ointments and powders, and ointments for treating diaper rash. Parents have been spreading zinc ointments directly onto the genitals of their babies, to cure diaper rash, for decades; this provides a valid indication of its absence of toxicity, and of its soothing and healing properties, when applied to the surface of the skin even in highly sensitive areas. Some topical forms sold over-the-counter contain more than 30% elemental zinc, by weight. Most topical forms contain zinc oxide, which gradually solubilizes and releases zinc ions when it contacts body fluids (Agren 1990).
In short-term tests, zinc has been shown to be harmless or beneficial inside the vagina (Chvapil et al 1978a and 1978b; also see Williams 1980 and Chvapil 1980). These reports describe research using guinea pigs, rabbits, and human volunteers to study whether zinc might be effective as a contraceptive. It was only about 80% effective on a single-event basis, so interest in contraceptive use died out; however, those reports indicated that (1) most of the zinc introduced into the vagina apparently became bound to vaginal fluids and exfoliated cells, and was washed out during the following days by the natural exudation of fluid from the vagina; (2) zinc content in vaginal tissue in treated animals was not significantly different than in control animals; and, (3) it did not cause any significant swelling, redness, tenderness, or histological changes to vaginal membranes. Indeed, when introduced into the vagina along with other contraceptive agents, zinc showed beneficial effects, by reducing or preventing the irritation or swelling caused by the other agents. This is consistent with the activity of zinc as a topical healing agent.
On the subject of vaginal tissue, it should be noted that the mucous membranes which coat the interior surfaces of the vaginal cavity are epithelial cells, rather than epidermal cells. Unlike epidermal cells, which lose their nuclei as they divide from basal cells below the epidermis, epithelial cells retain their nuclei as they approach and then reside on the outermost surface of a mucous membrane. However, those nuclei become attenuated and pyknotic, which means that the nuclei become inactive, compacted, and unable to carry out the normal chromosomal functions of replication and transcription.
Furthermore, epithelial cells remain on the surface for only a short period, and are constantly exfoliating (i.e., they detach and are shed by the membrane) and being replaced by new cells coming up from below. Reports such as Averette et al 1970 and Ferenczy and Guralnick 1979 state that inside the vagina, cells typically remain on the interior surfaces for only about 4 days before they detach and wash away. That period is even shorter in women being treated with hormones such as estrogen.
In healthy men, zinc is present in semen at concentrations of 100 to 500 ug/g, and in prostate fluid at concentrations up to 1000 ug/g (Eliasson and Lindholmer 1971; Fair et al 1976; Homonnai et al 1978; Marmar et al 1980). These concentrations are extraordinarily high compared to blood plasma, which contains only about 1 ug/ml zinc, and it indicates that dermal and epithelial membranes in the genital areas are adapted to withstand high concentrations of zinc. The roles and effects of these high concentrations are not fully understood; they apparently have some antimicrobial effects, and they also suppress the respiration (and therefore the metabolic activity and motility) of sperm cells (Eliasson 1971; Paz et al 1977). After ejaculation, sperm-associated zinc is diluted by other fluids, and it binds to various proteins inside the vagina. This reduces the concentration of sperm-associated zinc, allowing the activity and motility of the sperm to increase. The result, apparently, is that zinc provides a chemical method of keeping sperm cells in a quiet state, so they can conserve their energy until needed.
The high zinc concentrations in seminal fluid are relatively toxic to lymphocytes. This is not surprising, since zinc levels in blood are carefully regulated, and most lymphocytes never encounter the zinc concentrations that occur in semen. However, some lymphocytes do appear in ejaculates, and they apparently play an important role in transmission of HIV. The survival time of lymphocytes in ejaculates are likely to be longer in men suffering from AIDS-related reductions of the zinc levels in their semen (Weiner 1984 and Fabris et al 1988).
In this invention, the toxicity to lymphocytes of high levels of zinc in a topical lubricant apparently will be beneficial. HIV-infected lymphocytes appear to pose a greater threat of establishing an infection than free HIV particles; see Pearce-Pratt and Phillips 1993, Zagury et al 1985, Ho et al 1985, and Levy 1988. This increased risk is due to cell-cell binding reactions which allow infected lymphocytes to bind to and inject viruses into epithelial cells, which do not have CD4 receptors on their surfaces. By contrast, free HIV particles floating in a biological fluid can only infect cells that have CD4 receptors on their surfaces, and the viral particles must contact and bind to those particular receptors. Therefore, if non-physiologic concentrations of zinc in a topical lubricant used during intercourse can kill lymphocytes, this apparently would eliminate or reduce the ability of HIV-infected lymphocytes to establish cell-mediated infections in epithelial cells.
One object of this invention is to disclose an article of manufacture comprising a condom which is enclosed within a watertight package with a hydrophilic lubricant containing a non-irritating water-soluble zinc salt at a concentration that can reduce the risk that a previously uninfected person will become infected by a sexually transmitted virus such as herpes or possibly HIV.